Spring



' 1936. F. P. ZIMMERLI 2,055,315

' SPRING Filed March 20, 1931 INVENTOR. Fl Glenn VPick'weH BY Franz PZim'merIi A TTORNEYS.

Patented Oct. 6, 1936 V j i I 2,056,816

UNITED STATES PATENT OFFICE SPRING Franz P. Zimmerli, Detroit, Mich., assignor to The William D. Gibson Company, Chicago, 111., a corporation of Illinois Application March 20, 1931, Serial No. 523,962

' 9 Claims. (01. 261-61) This invention relates to a-spring. I tive signs. The degree of compression and ten- In either a coil spring or a fiat spring the greatsion is illustrated by the size of the positive and est stress due to loading is on the extreme outer negative signs. In other words, the greater the fibers. The stress on the fibers decreases as one plus sign the greater the compression to which approaches a definite area within the spring those fibers are subjected and the greater the which might roughly be defined as the center of negative sign the greater the tension to which the spring where the fibers are neither stressed those fibers are subjected. It will be noted, as nor compressed. With this fact in mind it is brought out by the large plus signs, that the exthe object of this invention to produce a spring treme outer layers of fibers adjacent the lower which will give an increased performance from surface 3 of the spring i are subjected to the 10 a given volume of material. This has been greatest compression as shown by the large posiachieved by raising the physical properties of the tive signs. This compression gradually decreases outer surface of the metals used in spring manuas one approaches the center 00 (Fig. 2) in facture. By strengthening these outer fibers and which theoretical area there is neither compresleaving the inner ones more ductile, a higher sion nor tension. This decrease in compression lo fatigue limit and greater spring life can be obas one approaches the center ll-0 is illustrated tained. I by the decrease in the size of the positive signs In the drawing toward the center of the spring. Fig. 1 is a view of a spring supported at one end Since, as above described, the tension and the showing the compression and tension of the compression is greatest on the extreme outer 20 Spring fl IS- fibers when the spring is loaded, it is proposed Fig. 2 is a section along the line 22 of Fig. l to make the extreme outer fibersof greatest tenillustrating the decrease in tension and compressional strength and gradually decrease the tension of the spring fibers as one approaches the sional strength. of the fibers as one approaches Center Of the Spring. the center of the spring 0-0 where theoretically 5 Fig. 3 is an illustrative view of a spring supthere is neither tension nor compression. The ported at two points with the load at the center. tensional strength of these outer fibers and the Fig. 4 is a section along the line 4 4 of Fig. 3 physical properties thereof may be raised in nulikewise illustrating the decrease in tension and merous ways such as by nitriding, case hardening,

compression as one approaches the center. or carbonizing steel springs. The strength ofthe 3 5 ShOWS an unloaded 1 p outer fibers could likewise be accomplished by Fig. 6 is a top plan view of the same. cold working of the metal. In any metal it could Fi 7 h ws the same coil spring loaded. be accomplished by a variation in analysis from Fig. 8 is a top plan view of the loaded spring center to outside. Showing the tension and mpression of the fibers This variation in analysis is brought out nicely 35 0f the p in Figs. 9, 10, and 11. In such a case an ingot Fig. 9 is a section through a composite ingot, is formed, the outer layers 4 of which may be of a center portion of which is of ductile material any metal having a high tensional strength such h pp and the uter portion of which as steel and the center portion 5 of this composite y besteelingot could be formed of any suitable ductile 4o Fig. 10 is a transverse section through the ingot. metal or composition of metals such as copper, Fig. 11 illustrates the method of rolling the zinc, or an alloy of the same. This ingot could Composite ingot into Wire 'mthen be put through suitable rolls such as are Since it is an object of the invention to proused in the production-of wire and rolled to induce a spring in which the physical strength of crease its length and' decrease its cross-sectional 45 the spring material varies in proportionto the area until in the form of a wire I of whatever tension and compression to which the spring fibers cross-sectional area desired. In such a. case the are subjected, there is shown in Fig. 1 afiat spring outer fibers 4 would be of great tensile strength I which is supported at one end only in the supand the center fibers 5 very ductile. In such a 5 port 2. In this instance the load L is applied at wire I, or in a leaf spring similarly formed, the '50 the outer end as shown by the arrow. In this outer fibers would be of greater physical strength instance the spring is bent downwardly. Consethan the inner ones which would be relatively quently, the lower fibers will be compressed as moreductile than the strong outer fibers. indicated by the positive signs and the upper In Fig. 3 there is shown the fiat spring 8 whichfibers will be tensioned as indicated by the negais supported at each end by the supports 9 and 55 III. The load L is applied intermediate the supports 9 and III. In such a case the upper fibers are compressed as indicated by the plus signs and the lower fibers tensioned as indicated by the negative signs. The degree of tension and compression is indicated by the size of the plus and the minus signs. This compression and tension gradually decreases towards the center --0 (Fig. 4) in which area there is neither tension nor compression. In such a spring likewise the fibers having the greatest .tensional strength would be those along the extreme outer surface indicated by the large plus and minus signs. The

tensional strength of the fibers would gradually decrease towards the center of the bar as indicated by the decrease in size and number of plus and minus signs approachingkthe center of the road. As shown in Fig. 8, when load L has been applied to the spring ii the fibers of the outer surface of the wire are placed in torsion and subject to clearing stresses, which are indicated by plus signs and vary from a maximum on the 'outer surface of the wire to a zero load at the center-of the wire. This loading is increased by imposed bending stresses which throw additional load on the wire. The samestress condition will hold good if instead of compressing the spring it were extended. In this instance likewise the outer fib'ers of the coil spring wire will benitrided, carbonized, case hardened, cold worked,

. or varied in analysis so that they will be of relaphysical properties and the fibers intervening those carrying the greatest stress and those car rying the least stress decreasing in tensional strength as theyv approach the fibers carrying the least stress or increasing in tensional strength as they approach the fibers carrying the greatest stress. More particularly, the invention contemplates a spring essentially characterized by an outer surface of great tensional strength and an inner area that is relatively ductile.

I claim:

1. A metal spring, the outer fibers of the entire surface of which are of greater tensional strength than the inner fibers.

2. A metal spring, the outer fibers of which completely surround the inner fibers and have relatively high physical properties and the inner fibers of which are relatively ductile.

3. A helical steel spring in which the outer fibers carrying the greatest stress have a higher tensional strength than, and completely surround, the inner fibers carrying the lesser stress.

4. A metal spring, the fibers of which vary in tensional strength from the outside to the center of the spring corresponding'to the stress to which they are subjected when the spring is loaded, the outer fibers having the greatest tensional strength and the inner neutral fibers having the least tensional strength.

5. A helical steel spring, the-outer fibers of which completely surround the inner fibers and have relatively high physical properties and the inner fibers of which are relatively ductile.

6. A metal spring, the extreme outer fibersof which are relatively strong and completely surround the inner fibers and the inner fibers relatively ductile.

7. A metal spring comprising an inner zone of relatively ductile fibers, an outer surface zone of fibers having relatively high physical properties, and a zone of fibers between the outer and inner zones wherein the fibers gradually decrease in tensional strength from the outer to the inner zones from the tensional strength of the outer zone fibers to the tensional strength of the relatively ductile fibers of the inner zone.

8.-A helical steel spring comprising an inner zone of relatively ductile fibers, an outer surface zone of fibers having relatively high physical properties completely surrounding and encasing the inner zone of fibers, and a zone of fibers intermediate the outer and inner zones wherein the fibers gradually decrease in tensional strength from the outer to the inner zones from the tensional strength of the outer zone fibers to the tensional strength of the relatively ductile fibers of the inner zone.

9. As an article of manufacture a nitridedsteel helical spring.

- FRANZ P. ZIMMERLI. 

